Colorectal cancer is the third most common cancer in the world. In Korea, colorectal cancer is the fourth most common cancer after stomach, lung and liver cancers in men, and is the third most common cancer after breast and stomach cancers in women. Recently, as Korean eating habits have become westernized, the incidence of colorectal cancer has increased rapidly in Korea. During recent 10 years in Korea, the mortality caused by colorectal cancer has increased by about 80% and showed a tendency to increase gradually (Korean Central Cancer Registry 2002). About 50% patients with colorectal cancer die within 5 years after diagnosis, and 15-25% of the patients are found to have liver metastasis at the time of diagnosis, and 20-30% of the patients are found to have liver metastasis during follow-up observation after surgery of primary colorectal cancer. Indeed, the cause of death of patients with malignant tumors, including colorectal cancer, is due to the metastasis of malignant tumors rather than the malignant tumors themselves.
Cancer-related studies have mostly been conducted on carcinogenic processes and mechanisms. In order to improve the treatment and survival rate of colorectal cancer patients, studies on colorectal cancer metastasis which is the most common cause of death are required, and among them, studies on the metastasis of colorectal cancer to the liver that is the most common metastasis site are necessary.
In many studies conducted to date, a microarray gene expression profiling technique has been used to discover biomarkers related to the occurrence or metastasis of malignant tumors. Although this technique allows the expression of whole genes to be determined, it is difficult to carry out, is very expensive and has high false-positivity. Also, additional processes of examining the expression levels of genes by Northern blotting, RT-PCR and the like should be performed after the test. The RT2 Profiler PCR Array comprises a 96-well plate containing SYBR Green-optimized primer sets for genes classified according to pathway (e.g., apoptosis, cell cycle, cancer, signal pathway, etc.) or disease and can analyze the expression of a group of groups involved in a specific signal pathway using a real time PCR-based technique.
Accordingly, the present inventors have made extensive efforts to develop a biomarker capable of diagnosing the liver metastasis of colorectal cancer and, as a result, have found that, when the mRNA expression level of CCL7 gene and the level of CCL7 protein are compared between the liver metastasis site of colorectal cancer and the primary site of colorectal cancer, the mRNA level of the CCL7 gene is more strongly expressed at the liver metastasis site and the level of the CCL7 protein is also higher at the liver metastasis site, suggesting that the CCL7 gene can be used as a biomarker specific for liver metastasis of colorectal cancer, thereby completing the present invention.